IN ITS HEYDAY, THE SR-71 BLACKBIRD WAS ONE bodacious spy plane. Pilots who flew it say it could go higher and faster than anything this side of the space shuttle, leaving enemy missiles behind like slugs on the patio. Blackbird reconnaissance flights over hot spots like North Korea, Vietnam, Cuba, Libya and Iran are the stuff of legends; not a single one of the rakish jets was lost to hostile fire.

But Pentagon bean counters figure that modern spy satellites can take photos of anything on earth -- and for a lot less money. So the SR-71s have become high-tech relics. Fortunately, the Smithsonian's National Air and Space Museum has gotten its hands on one.

"The Air Force flew this Blackbird -- number 17972 -- to Dulles last March 6, setting a world speed record from Los Angeles to Washington doing it," says museum specialist Ed Marshall, unlocking the gate to a chain-link fence that protects the exotic aircraft while it's stored in a lightly traveled area of Dulles, about a mile south of the main terminal. Marshall, who was on the seven-man crew that prepared the Blackbird for storage and eventual display, says the Air Force was quite generous, throwing in an extra set of tires, a spare engine and scads of maintenance equipment. But a few things were held back -- some for safety reasons, some because certain information about the Blackbird is still classified even after nearly 30 years.

"They removed explosive cartridges from the ejection seat and kept the original battery. Some time-distance placards from the cockpit were also removed," Marshall says. "A digital mission recorder was replaced with a non-serviceable one, and we exchanged an astro-inertial navigation system with radioactive carbon-14 for one that emitted less radiation. To an observer, though, the aircraft appears complete."

One would think that the SR-71, which can fly faster than a rifle bullet and endure friction-generated temperatures of more than 800 degrees Fahrenheit, would be pretty tough. But Marshall says it has to be handled with TLC.

Towing it around presents special problems.

"The SR-71 was designed to land on a perfectly smooth runway," says Marshall. "Its tires are inflated to almost 300 pounds pressure, so pebbles as small as a pea can do real damage."

The Blackbird faces other dangers on the ground.

"Constant exposure to sun and rain tends to damage any aircraft, and the Blackbird is no exception," Marshall says. "We'd like to move it into a building for security and preservation until the Air and Space Museum's Dulles extension opens in 1995. But we're still seeking funding for that."

Then there's the matter of the birds.

White droppings have been spattering the SR-71's matte black titanium alloy skin. But Marshall says a temporary solution has been found: A $10 plastic owl, strategically placed on the Blackbird's wing, has scared them away.